A cylindrical lock is commonly divided into a trumpet lock and a tubular lock. The main difference between both locks is that the latter is locked or unlocked by turning a turning button and the dead bolt is directly moved by the tubular shaft of the inside or the outside knob, and the former is locked by pressing a button and the dead bolt is moved by the latch retractor. Therefore, both the locks have difference in their structure and the shape of the knobs. Subsequently, makers have to be equipped with two different sets of molds for production.
In addition, conventional tubular locks have a drawback by which they can easily be unlocked stealthily owing to their unsteady locking movement For example, that of an U.S. patent titled "Holding device for a lockset", Ser. No. 3,556,576 dated Jan. 19, 1971, has a comparatively strong structure, but it still has the disadvantage just described. Besides, the inside knob cannot be turned to unlock the lock after the lock is locked. So in practical use, the tubular lock has evidently worse function than the trumpet lock, and consequently is less widely used.